1) Field of the Invention
The present invention generally relates to an image formation apparatus such as an electrophotographic recording apparatus including a toner image carrying body such as a photosensitive drum, a dielectric drum or the like to which a toner image obtained from toner development of an electrostatic latent image is electrostatically adhered and held, and from which the toner image is electrostatically transferred to a recording medium such as a sheet of paper, and in particular, relates to a toner image fixing device incorporated therein for thermally fusing and fixing the toner image on the recording medium.
2) Description of the Related Art
As a representative example of the image formation apparatus as mentioned above, an electrophotographic recording apparatus is well known, wherein the following processes are typically carried out:
a) a uniform distribution of electrical charges is produced on a surface of an electrostatic latent image carrying body;
b) an electrostatic latent image is formed on a charged area of the body surface by an optical writing means such as a laser beam scanner, an LED (light emitting diode) array, a liquid crystal shutter array or the like;
c) the latent image is developed as a visible image with a developer or toner, which is electrically charged to be electrostatically adhered to the latent image zone;
d) the developed and charged toner image is electrostatically transferred from the body to a recording medium such as a sheet of paper; and
e) the transferred toner image is fixed and recorded on the paper.
Typically, the electrostatic latent image carrying body may be an electrophotographic photoreceptor, usually formed as a drum, called a photosensitive drum, having a cylindrical conductive substrate formed of a metal such as aluminum, and a photoconductive insulating film bonded to a cylindrical surface thereof and formed of an organic photoconductor (OPC), a selenium photoconductor or the like.
In the toner image fixing process, a heat roller type toner image fixing device is widely used, which comprises a heat roller, and a backup roller engaged with the heat roller to form a nip therebetween, and a sheet of paper carrying a toner image is passed through the nip in such a manner that the toner image is in direct contact with the heat roller, whereby the toner image is thermally fused and fixed on the paper. During the passage of the paper through the nip between the rollers, a small part of the fused toner is adhered to a surface of the heat roller, and, when no sheet of paper is passed through the nip, the toner adhered thereto is partially transfered to the backup roller. Of course, the fused toner adhered to the rollers stains sheets of paper which are successively fed to the toner fixing device.
For this reason, conventionally, a cleaning member is applied to the heat roller to remove the fused toner adhered thereto. As one type of cleaning member, a bar type cleaning member is well known, which includes an elongated bar element and a cleaning element attached thereto and made of a suitable cleaning material such as felt. The bar type cleaning member is provided in the fixing device such that the felt element is pressed against the surface of the heat roller, whereby a removal of the fused toner from the heat roller can be carried out. Nevertheless, this type of cleaning member must be frequently exchanged with a new one, because the cleaning area of the felt element is small.
As another type of cleaning member, a roller type cleaning member is also well known, which includes a shaft element, and a cleaning roller element mounted thereon and made of a cleaning material such as felt. The roller type cleaning member is provided in the fixing device such that the roller element is pressed against the surface of the heat roller. During the cleaning, the roller type cleaning member is rotated to remove the fused toner from the heat roller. This type cleaning member has a larger cleaning area than that of the bar type cleaning member, and thus frequency of exchanging the cleaning member is considerably low in comparison with the bar type cleaning member. Nevertheless, the exchange of the roller type cleaning member is troublesome because the shaft element of the cleaning member is supported at the ends thereof by a pair of bearings attached to a frame of the fixing device.